The problem with living cells is that they “age,” that is to say, with the passage of time they begin to literally fall apart to the point that the mechanism of life can no longer be sustained – and what was once animate becomes inanimate. Life gives way to death and, absent the late night laboratory perambulations of a latter day Victor Frankenstein, the process admits of no reversal. But what if the process could be suspended? What would happen if a living organism could literally be frozen in time only to “reanimate” itself at a later date?
Strange as it sounds, the answer may lie with the common wood frog (Rana sylvatica), which has the ability to freeze almost solid for months at a time in winter, only to thaw out and resume its living activities during the warmth of spring. But how does it do this?
The process is neither simple nor easy:
Similar to other northern frogs that hibernate close to the surface in soil and/or leaf litter, wood frogs can tolerate the freezing of their blood and other tissues. Urea is accumulated in tissues in preparation for overwintering, and liver glycogen is converted in large quantities to glucose in response to internal ice formation. Both urea and glucose act as “cryoprotectants” to limit the amount of ice that forms and to reduce osmotic shrinkage of cells. Frogs can survive many freeze/thaw events during winter if not more than about 65% of the total body water freezes.
Six years ago, the PBS science program NOVA investigated this bizarre natural phenomenon. Robert Krulwich interviewed biologist Joe Costanzo and presented this report:
And now for the money quote:
ROBERT KRULWICH: It’s harder for water to freeze, so cells stay just damp enough for the animal to hold itself together, until the springtime, when the days grow a little longer and the ground gets a little warmer and then, well, a kind of miracle happens: After weeks or months of no heartbeat – none – suddenly there’s a pulse. And that first heartbeat leads to another and then another and then, within a day, and—in the case of this little frog, it took about 10 hours—the animal literally comes back to life.
JOHN COSTANZO: Spontaneous resumption of function.
ROBERT KRULWICH: Why?
JOHN COSTANZO: We don’t know. We don’t know what triggers that event.
That is to say, the empiricist doesn’t know. For my part, I can guess.